Particle accelerators are apparatuses that are used for accelerating subatomic particles to high velocities by means of electric or electromagnetic fields. When particles are accelerated to reach a specific energy, they are used for treatment of patients with malignant tumors. The particles may be accelerated either in a straight line, in which the particles are accelerated within a specific distance, or the particles may be accelerated in a circular accelerator. The circular accelerator moves clusters of particles in a circle (or oval), and with each completion of the circle, the cluster of particles gains energy until the particles have reached sufficient energy levels, at which point the particles may be extracted and directed to the tumor.
Extraction is the process of removing a particle beam from the accelerator to a transfer line or a beam dump, at the appropriate time, while minimizing the beam loss, and placing the extracted particles into a desired trajectory. One method of extracting a proton particle beam is described in U.S. Pat. No. 7,432,516, the content of which is incorporated herein by reference in its entirety. The method includes initiating a kicker magnet which turns on a vertical magnetic field that moves the particle beam horizontally towards a septum magnet which further bends the beam horizontally and away from the accelerator and into a beam line which guides the beam to the tumor of the patient. However, due to limitations on the level of radiation acceptable to a patient, and challenges in accelerating and controlling low numbers of carbon particles in the accelerator, such extraction methods may be less suitable for carbon particles. Another method of extracting a particle beam is described in U.S. Pat. Nos. 8,415,643 and 8,399,866. The method includes passing the beam through a radio-frequency cavity system to induce oscillation of a charged particle stream. With sufficient amplitude modulation the particles hit an energy reducing foil which decreases the energy of the charged particle stream and decreases the radius of curvature sufficiently to allow physical separation of the reduced-energy particle stream from the original particle stream. However, with this method, not only may the extracted particle beam have less energy than the original beam, the extracted particle beam may also have a higher energy spread resulting in less precision of the particle beam. Furthermore, this method may also result in beam particle loss as well as residual activity in the relatively thick energy reducing foil.
Therefore, there is a need for an apparatus and method which may be used on the extraction of carbon particle beams while maintaining the energy levels and precision of the particles and the particle beam.